Inflight Service / service on transit

I would like to raise up my complaint regarding the service in your flight when i going to Malaysia for holiday. I have made my booking on March'09 and have choose the seat during my booking. Unfortunately when i on board on the flight our seats is change for twice. My flight is EK004 and EK342, my seats is change on the flight EK342 seat is 24D and 24E, then we change to 24G, 24H, during the flight nearly take off they change our seats to 23D and 23E. I dont' know why your airline let choose our seats and they change it on the flight. This is the first time I travel with Emirates airline but it is really let down. I have no any confidence on your airline. I hope during my return to UK your airline will provide a good service. Thank you.